Metallurgical processes such as basic oxygen steelmaking often employ large (typically, about 8 inches to about 16 inches in diameter and approximately 65-85 feet long) water-cooled oxygen lances to efficiently remove oxidizable elements from molten metal in a metallurgical converter. These lances, which typically weigh up to approximately 10 tons, are known as post-combustion lances. Typically, in addition to the primary oxygen ports at the tip of the lance, the prior art post-combustion lance includes a ring of small oxygen ports located on the outside of the lance a distance up the lance from the primary oxygen tip. The ring is known as a post-combustion (or “PC”) distributor.
Due to heat transfer requirements, and also to protect the PC distributor from the furnace atmosphere and the localized heat generated from the post-combustion reaction, the PC distributor (and often, the piping associated therewith) is made of high thermal conductivity metals such as high purity copper.
Although the post-combustion lance often is used to direct oxygen into a metallurgical converter, various other gases may be directed through the lance, depending on the reactions desired. Any and all reaction gases directed through the lance are generally referred to hereinafter as a “gas” for convenience, it being understood that the gas may be oxygen or any other reaction gas or gases. Typically, the gas is injected through the lance at very high rates. For example, oxygen may be injected into the lance at rates of between 300 cubic meters/min. and 600 cubic meters/min.
Cross-sections of a typical post-combustion lance 10 of the prior art are provided in FIGS. 1A and 1B. (The balance of the drawings disclose the invention herein.)
The lance 10 extends between an upstream end 12, at which the gas is introduced therein, and a downstream end 14, at which a primary tip 16 is positioned. The introduction of the gas at the upstream end is represented by arrow “A” in FIG. 1A. A PC distributor 18 is positioned at a predetermined distance from the tip 16. The typical lance includes a lance body 20 having an upper portion 22 and a lower portion 24. The upper portion 22 typically has slightly larger inner and outer diameters than those of the lower portion 24 respectively. The body 20 includes the PC distributor 18, which is mounted between the upper and lower portions 22, 24, as shown in FIG. 1B. Typically, the upper and lower portions 22, 24 are substantially round in cross-section, i.e., they are generally cylindrical.
As shown in FIGS. 1A and 1B, the prior art post-combustion lance 10 typically (but not necessarily) also includes an upper inner tube 26 with an upstream portion 28, a larger second portion 30, and a connecting portion 32 connecting the first and second portions 28, 30. Also, a lower inner tube 34 is positioned inside the body 20, downstream from the upper inner tube 26. Typically, the upper and lower inner tubes 26, 34 are positioned coaxial with each other and with the body 20. The upper and lower inner tubes 26, 34 are shaped to direct part of the gas to the PC distributor 18, and also to direct a part of the gas toward the lower inner tube 34, from which such portion exits the lance at the tip 16. For example, the first part of the gas typically may be about ten percent of the gas flowing through the lance, with the second part being the balance. The part of the gas exiting the PC distributor is represented by arrows “B” in FIG. 1A, and the part of the gas exiting the tip 16 is represented by arrow “C” in FIG. 1A.
As is well known in the art, the upper and lower portions 22, 24 typically include cavities 25 through which water (not shown) is circulated while the post-combustion lance 10 is in use, to cool the lance body 20. Typically, the water is introduced at the upstream end 12 into an intake cavity which extends to the downstream end 14 and the primary tip 16, and the water returns to the upstream end 14 via an output cavity. As is also well known in the art, both the upper inner tube 26 and the lower inner tube 34 are secured to the body. The upper and lower portions 22, 24 are substantially cylindrical, and positioned substantially coaxial with each other. For instance, the axes defined by the upper and lower portions 22, 24 are identified by reference numeral 27 in FIG. 1B. In addition, the upper inner tube 26 typically is positioned substantially coaxial with the upper and lower portions 22, 24. Also, in the prior art lances in which the lower inner tube 34 is included, the lower inner tube 34 (which typically is substantially cylindrical) typically is positioned substantially coaxial with the upper and lower portions 22, 24 and with the upper inner tube 26. It will be understood that various prior art lances are known.
The lance is subjected to bending stresses during its service life, particularly during loading and unloading operations and during lance deskulling operations, where steel and slag buildup on the lance exterior surfaces 36 is removed using aggressive mechanical means, including, e.g., machinery employing hydraulic and/or pneumatic hammers and steel tips. When in use, the lance typically is supported only at the upper portion (i.e., above the distributor). Accordingly, the prior art lance typically is subject to deflection (i.e., substantially or at least partially transverse deflection) due to the bending stresses to which it is subjected. For example, the prior art lance 10 in FIG. 1B may be urged to deflect transversely (i.e., relative to the axes 27) by downward deflection of the lower portion relative to the upper portion, as indicated by arrow “D” in FIG. 1B.
Lances equipped with the PC distributor typically are prone to severe bending (i.e., deflection) and, in some cases, failure at the PC distributor, because of the relatively low yield strength of the high thermal conductivity components in the PC distributor. Since the introduction of the mid-lance PC distributor (i.e., at least in the 1980s, and possibly earlier), no effective solutions to the bending and/or failure problems have been implemented. Prior art post-combustion lances typically bend after a relatively short period in service, requiring relatively frequent replacement of the PC distributor.
Previous attempts to address this problem included the development of external removable protective sleeves which are put on new and refurbished PC distributor equipped lances to protect the lances during shipping to the user's facilities. However, the protective sleeves must be removed before the lance is put into service. In practice, sleeves are typically removed prior to completion of the unloading and installation of the lance. As a result, the lance is often bent subsequent to the protective sleeve removal, i.e., during the completion of installation, while in service, or while the lance is loaded back onto the truck for return repair at the end of its service life.